L7 gto

Part of Lecture series on EE321N, Power Electronics-I delivered by me during Fifth Semester of B.Tech. Electrical Engg., 2012
Z H College of Engg. & Technology, Aligarh Muslim University, Aligarh
Please comment and feel free to ask anything related. Thanks!

1. EE‐321 N
Lecture ‐7
Gate Turn OFF (GTO) Thyristor

2. Introduction
•TheconventionalSCRistherulingdevicefor
the power electronics industry due to very
highratings
•However, it is asemi ‐controlleddevice
because it can’t be turned OFF by the gate
terminal
•GTO achieves this objective of being turned
OFFby–vegatecurrentandthusisafully
controlledswitch 27‐Jun‐15EE‐321N,  Lec‐72

3. Contd...
•Twoconfigurationsavailable:asymmetricand
symmetric
•Availableratingsupto:6kV,6kA(Mitsubishi) 27‐Jun‐15EE‐321N,  Lec‐73
Popular

4. Device Symbol

5. Structure
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6. Contd...
•TurnOFFcapabilitybysupplying–veI
G
canbe
guaranteed if the access resistance from the
gatetoallpartsofthedevicecathodeisvery
low
•This is done by using an “interdigitated”
structure in which the gate‐cathode area is
distributed over the whole pellet and
interleavingtheirrespectiveregions
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7. InterdigitizedStructure
(Front View)
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8. InterdigitizedStructure
(Top View)
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Cathode
Gate

9. Appearance
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10. Characteristics
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RealIdeal

11. Turn OFF Mechanism  
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12. Remember ?
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13. Analysis
•AbovecircuitwasusedtoexplaintheturnON
mechanismofSCR
•Nowweusethistounderstandhowturn‐OFF
isachieved
•Bothtransistorsareinsaturation
•A –ve gate current can bring T
2
out of
saturation and eliminate this “regenerative”
effecttherebyturningOFFthedevice
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14. Contd...
•The anode  current  is given  by:
•Suppose, we neglect I
CBO
’s then I
A
= 0 means 
that 
27‐Jun‐15EE‐321N,  Lec‐714
)(1
21
2 1 2
αα
α
+−
++
=
CBO CBO G
A
III
I
(
)
2 2
12 12
1( )1( )
G G
A
I I
I
α α
α
ααα
− −
==
−+ −+

15. Contd...
•Turn‐OFFgainβ
OFF
fortheturn‐OFFprocessof
aGTOisdefinedas:
•β
OFF
liesintherange4‐5(low)butthiscallsfor
averyhigh–I
G
.E.g.ifI
A
=2000Athen–I
G
=
500A(around)
•A high value ofβ
OFF
can be obtained by
makingα
2
highandα
1
low
27‐Jun‐15EE‐321N,  Lec‐715
()
2
OFF
12
1
A
G
I
I
α
β
αα
==
+−

16. Comparison with Conventional SCR
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17. AdvantagesDisadvantages
Elimination of commutating
components in forced commutation
resulting in reduction in cost, weight
andvolume.
ON state voltage drop and associated
losses are higher in GTO than
thyristor
Reduction  in acoustic and 
electromagnetic noise due to the
elimination of commutation  chokes
Triggering gate current required for
GTOsismorethanthoseofthyristor
Faster turn OFF permitting high
switching frequency
Latching and holding current is more
inGTOthanthoseofthyristor
Improved converters efficiencyGatedrivecircuitlossismorethan
thoseofthyristor,and,
It has more di/dtrating at turn ONItsreversevoltageblockcapabilityis
lessthanitsforwardblocking
capability.(Butthisisnodisadvantage
forinverters/choppers)
17 27‐Jun‐15EE‐321N,  Lec‐7

18. HOME  ASSIGNMENT
Q1.DiscusstheswitchingcharacteristicsofSCR.
Emphasize on the following terms: Delay
time,risetime,spreadtime,turn‐OFFtime,
circuitturnOFFtime.
Q2.Discussbrieflyotherdevicesofthethyristor
family. Highlight their circuit symbol,
characteristics, ideal characteristics, main
applications
27‐Jun‐15EE‐321N,  Lec‐718

19. Reminder
•Internet connection is now available
•Please  complete the Today’s Task assigned in 
lecture‐2
•Will be checked  randomly 27‐Jun‐1519 EE‐321N,  Lec‐7

20. End of Unit‐1
27‐Jun‐15EE‐321N,  Lec‐720
☺